The use of milled silica hydrogels as a total system for both filtering out solids from alcoholic fermented beverages and obtaining chill-haze proof stabilised beverages is well known, and is disclosed by Clark et al; M.B.A.A. meeting Winnipeg 1980 (The Brewer June 1980 p168). This article describes the use of silica hydrogels manufactured to defined specifications as a complete replacement for Kieselguhr and/or Perlite.
The advantages of a total hydrogel filtration system over the traditional one based on Kieselguhr or Perlite apart from its dual performance characteristic are:
(i) the material is less abrasive; PA1 (ii) fine particulate silica hydrogel is non-dusting; PA1 (iii) freedom from using hazardous components; and increased filter cake density which provides PA1 (iv) increased filter cake density which provides increased filter capacity. PA1 H=Bed Depth (cms). PA1 *u=Viscosity mpas. PA1 *A=Cross sectional area of tube (cm.sup.2). PA1 *DP=Pressure differential across bed (atmos). PA1 *For a given apparatus these parameters are constants.
The original concept of the total hydrogel system was based on varying the particle size and controlling the particle size distribution of the milled silica hydrogel to produce a range of products that would meet the majority of filtration requirements. An equivalent product to pre-coat grade Kieselguhr and Perlite would have a large particle size (about 40 micron) and a permeability (defined later) of above 0.5 Darcies, whereas a replacement for the body feed-types would be finer (particle size about 15 micron), and have a permeability of 0.1 to 0.3 Darcies. The Clark et al article discusses Darcies as a measure of permeability.
The coarse particle size milled silica hydrogel precoat product has been found to have disadvantages over the traditional filter materials, particularly when used on candle filters. Owing to its much higher particle density of 1.2 kg/liter when compared with Kieselguhr and Perlite, 0.7 and 0.4 kg/liter respectively, the coarser milled silica hydrogel product failed to coat the filter uniformly giving rise to varying pressure drop along the length of the filtration element and the subsequently observed poor filtration performance with respect to running time and clarity of the alcoholic beverage.
The present invention provides improvements in the use of precoated fillers for the treatment of alcoholic beverages. These filters are described in Brewing Science vol. 3 Academic Press Inc. (London) 1987 in particular in chapter 3.6 (J. Posada).